This application claims the benefit of a Japanese Patent Application No. 2001-133675 filed Apr. 27, 2001, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to optical modules and optical module producing methods, and more particularly to an optical module, having an optical connector, which is detachably and optically coupled and is covered by a molded resin for protection at the time of production, and to an optical module producing method for producing such an optical module.
2. Description of the Related Art
In optical communication apparatuses and information processing apparatuses which process optical signals, there are demands to realize a high-density optical signal transmission at a high speed and a high capacity. On the other hand, there are also demands to reduce the size and cost and to simplify the structure of a transmitter section and a receiver section of a terminal equipment which transmits and receives the optical signal. Hence, there are similar demands with respect to various kinds of optical modules.
In the optical module which is coupled to an optical fiber of the transmission line, it is desirable that the optical module is detachably connected directly by an optical connector. Hence, the so-called pig-tail type optical module, which has the optical connector at a tip end of an optical fiber having a suitable length, is popularly used. However, the provision of the optical fiber introduces various problems.
For example, when assembling the optical module by an automatic assembling process, the provision of the optical fiber interferes with the full automation of the assembling process. In addition, when transporting the optical module, it is necessary to accommodate the optical module within a transporting case and to handle the optical module with care. Furthermore, when mounting a main body of the optical module within an apparatus, it is necessary to take appropriate measures such as mounting the optical fiber by winding the optical fiber to a predetermined diameter.
In view of the above, it is possible to effectively reduce the size of the optical module, by providing an optical connector section without via an optical fiber, as shown in a cross sectional view of FIG. 1.
An optical module 1 has a projecting ferrule 2, for an optical connector, provided with an optical fiber at a central portion on a tip end portion on the left side of the optical module 1 in FIG. 1. The periphery of the ferrule 2 fits in a first cylindrical member 3, and the periphery of the first cylindrical member 3 fits in a second cylindrical member 4. An end surface of the second cylindrical member 4 is connected to an end surface of an optical device 5 which is made of a sealed container. An optical element, such as a laser diode which is used as a light emitting element, is provided within the optical device 5.
A plurality of terminals 6 for connecting to electrical circuits is provided on the right side of the optical device 5 in FIG. 1. The terminals 6 are connected to a circuit board 7 having various electrical circuits. Terminals 8 for connecting to an external circuit are provided on both sides of the circuit board 7.
A synthetic resin molded portion 9 covers, that is, encapsulates, the periphery of the optical module 1, excluding the tip end portion of the ferrule 2 and the ends of the terminals 8, to form the optical module 1.
The synthetic resin molded portion 9 has an engaging part 11 which projects on both sides in a direction perpendicular to an axis direction of the ferrule 2 and the first cylindrical member 3. The engaging part 11 includes a sloping surface 12 located on a left side in FIG. 1, an engaging surface 13 perpendicular to the axis direction located on the right of the sloping surface 12, a flat guide portion 14 located on the left of the sloping surface 12, and a constricted portion 15 located on the right of the engaging surface 13. These elements of the engaging part 11 form a connector section 16 of the optical module 1.
In FIG. 1, the cross section of the synthetic resin molded portion 9 is shown along the solid line to facilitate understanding of the positional relationship of the optical device 5 and the circuit board 7.
FIGS. 2A and 2B respectively show a plan view and a cross sectional view of an optical connector 21 of an optical fiber cord which forms an optical fiber transmission line that connected to the optical module 1. In the optical connector 21, a cylindrically coiled spring 24 having a slit 23 in the axis direction, and also referred to as a split sleeve, is fit into a central penetration hole in a synthetic resin molded housing 22. A ferrule 25 is press-fit within the cylindrically coiled spring 24 so as to push and spread the diameter of the cylindrically coiled spring 24.
A holder 26 is press-fit and connected to the left side of the ferrule 25 in FIGS. 2A and 2B. An optical fiber cord 27 is fixed to the holder 26. In addition, the optical fiber of the optical fiber cord 27 penetrates the center of the ferrule 25 and is connected to the ferrule 25. The end of the optical fiber is exposed at the end portion of the ferrule 25, and is optically polished.
A compressed coil spring 28 is inserted between the housing 22 and the holder 26. The compressed coil spring 28, together with the holder 26, pushes against the ferrule 25 and urges the ferrule 25 towards the rightward direction in FIGS. 2A and 2B.
A pair of engaging leaf springs 31 which project towards the axis direction are provided in parallel on the right side of the housing 22 in FIGS. 2A and 2B. Each engaging leaf spring 31 has an engaging projection 32 on a tip end thereof, and a guide portion 33 on an inner side of the engaging projection 32. The engaging projections 32 of the pair of engaging leaf springs 31 confront each other, and the guide portions 33 of the pair of engaging leaf springs 31 confront each other.
A sloping surface 34 and an engaging surface 35 which is perpendicular to the axis direction are formed on the tip end of the engaging projection 32. The engaging projection 32 and the guide portion 33 are separated by an intermediate space or gap which extends in a direction perpendicular to the paper in FIGS. 2A and 2B.
The optical connector 21 is known as an EZ type optical connector, and the diameter of the ferrule 25 is 1.25 mm. The housing 22 is made of a synthetic resin having mechanical resilience. The cylindrically coiled spring 24 is made of a resilient material such as zirconia ceramics or metal. The ferrule 25 is made of zirconia ceramics. The holder 26 is made of a molded synthetic resin, and the compressed coil spring 28 is made of a known metal coil.
When optically connecting the optical module 1 and the optical connector 21, the engaging projection 32 of the optical connector 21 is fit over the connector section 16 of the optical module 1, as shown in FIG. 3A which shows the optical connector 21 in cross section.
In other words, the optical connector 21 is pushed so that the guide portions 14 fit into the intermediate spaces of the upper and lower engaging projections 32. Hence, the sloping surfaces 12 and 34 contact each other, and the engaging leaf springs 31 of the optical connector 21 are spread on both sides against the spring force by this contact. As a result, the engaging projections 32 fit into the constricted portions 15 of the connector section 16 as shown in FIG. 3B, and the engaging leaf springs 31 are restored to their original states by the spring force.
During the above process, the tip end of the ferrule 2 fits into the cylindrically coiled spring 24 against the spring force of the cylindrically coiled spring 24. Hence, the tip end of the ferrule 2 is positioned to the central position of the cylindrically coiled spring 24, and the center of the tip end of the ferrule 2 matches the center of the tip end of the ferrule 25 of the optical connector 21. Furthermore, since the tip end of the ferrule 2 moves while compressing the compressed coil spring 28, the tip end of the ferrule 25 is pushed against the tip end of the ferrule 2 by the action of the compressed coil spring 28, to thereby realize a positive optical connection between the ferrules 2 and 25.
In addition, the guide portions 14 of the optical module 1 and the guide portions 33 of the optical connector 21 engage each other to maintain the optical module 1 and the optical connector 21 in a stable connected position. The engaging surfaces 35 of the optical connector 21 contact and engage the engaging surfaces 13 of the optical module 1, so as to positively prevent the optical module 1 and the optical connector 21 from slipping off from each other, and to provide the required optical coupling.
When disconnecting the optical module 1 and the optical connector 21, the engaging projection 32 on the tip ends of the engaging leaf springs 31 are spread with respect to the connector section 16 of the optical module 1, and the optical connector 21 is then pulled from the optical module 1. Since the optical connector 21 is small, the engaging leaf springs 31 are spread by use of an exclusive spreading jig.
Next, a description will be given of the method of assembling the ferrule 2 and the optical device 5 of the optical module 1, by referring to FIG. 4 which shows a cross section of these elements. In FIG. 4, the first cylindrical member 3 is press-fit and positioned on the periphery of the ferrule 2, and the second cylindrical member 4 is fit on the periphery of the first cylindrical member 3.
The end surface of the second cylindrical member 4 contacts and connects to the end surface of a sealed container of the optical device 5. A laser diode (LD, not shown) is provided as an optical element at a central bottom portion on the right end of the sealed container of the optical device 5. A light transmitting window is provided in the sealed container of the optical device 5 at a position confronting the optical fiber 36 which is provided at the center of the ferrule 2. A spherical lens 37 which forms a light transmitting optical system is mounted at the light transmitting window maintaining the sealed state of the sealed container of the optical device 5.
When assembling each of the above described elements, the second cylindrical member 4 and the first cylindrical member 3 are positioned along the axis direction so that the relative positional relationship via the spherical lens 37 optically match between the laser diode mounted on the sealed container of the optical device 5 and the end surface of the optical fiber 36 of the ferrule 2. In addition, the end surface of the second cylindrical member 4 and the end surface of the sealed container of the optical device 5 are positioned and fixed.
The above described positioning is made while measuring the optical output of the laser diode as the output from the optical fiber 36, so that the measured output becomes a maximum. In this state, a contact portion 38 between the first cylindrical member 3 and the second cylindrical member 4 and a contact portion 39 between the second cylindrical member 4 and the sealed container of the optical device 5 are welded by irradiating a welding laser beam from a plurality of symmetrical surrounding locations with respect to the center axis and instantaneously fixed with a satisfactory precision, without introducing positional error.
Thereafter, the circuit board 7 is connected to the above described assembled elements and placed in a cavity within a mold having a predetermined shape, so that the tip end of the ferrule 2 and the tip ends of the terminals 8 project by predetermined distances from the cavity. A synthetic resin such as an epoxy resin in a melted state is supplied into the cavity of the mold, and the synthetic resin molded portion 9 shown in FIG. 1 is removed from the mold after curing.
As shown in FIG. 1, the synthetic resin molded portion 9 covers the periphery of the first cylindrical member 3, the second cylindrical member 4 and the optical device 5, including the periphery of the ferrule 2. But when the melted synthetic resin is supplied into the cavity of the mold, volatile gas is generated from the melted synthetic resin which is at a temperature of 180xc2x0 C. and is in a high pressure state. This volatile gas enters into a minute gap between the first cylindrical member 3 and the second cylindrical member 4, a minute gap between the second cylindrical member 4 and the sealed container of the optical device 5, and a space between the ferrule 2 and the spherical lens 37 which confront each other.
When the synthetic resin molded portion 9 is removed from the mold, the volatile gas solidifies and forms a thin film on the surfaces of the optical fiber 36 and the spherical lens 37. An optical coupling loss occurs when such a thin film is formed, and consequently, a desired optical characteristic cannot be obtained.
Accordingly, it is a general object of the present invention to provide a novel and useful optical module and optical module producing method, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide an optical module and an optical module producing method, which can protect an optical coupling part so that the problems described above are eliminated, and a desired optical characteristic can be obtained.
Still another object of the present invention is to provide an optical module comprising a ferrule an optical fiber which penetrates a center thereof along an axis direction of the ferrule; a member inserted with the ferrule; a sealed container, connected to the member, having an optical system which optically couples to the optical fiber; a resin portion encapsulating the member and the sealed container; and a communication path including a first communication passage between the ferrule and the member, a space where the optical system and the optical fiber confront each other, and a second communication passage between the ferrule and the member, where the first and second communication passages are mutually independent. According to the optical module of the present invention, it is possible to use the communication path to supply a gas when molding the resin portion, so that fine particles of a volatile gas generated from the melted resin are prevented from adhering to the optical fiber and the optical system and forming a film when the volatile gas solidifies. For this reason, it is possible to prevent deterioration of the optical coupling between the optical fiber and the optical system, and the optical coupling part of the optical module is positively protected.
In the optical module, the first and second communication passages may be provided in at least one of the ferrule and the member.
A further object of the present invention is to provide an optical module producing method for producing an optical module which is provided with a ferrule an optical fiber which penetrates a center thereof along an axis direction of the ferrule, a member inserted with the ferrule, a sealed container connected to the member and having an optical system which optically couples to the optical fiber, a resin portion encapsulating the member and the sealed container, and a communication path including a first communication passage between the ferrule and the member, a space where the optical system and the optical fiber confront each other, and a second communication passage between the ferrule and the member, where the first and second communication passages are mutually independent and the optical module producing method comprises the step of (a) placing at least the ferrule and the member within a mold; and (b) supplying a gas to the first communication passage and exhausting the gas from the second communication passage when supplying melted resin into the mold to form the resin portion. According to the optical module producing method of the present invention, it is possible to use the communication path to supply a gas when molding the resin portion, so that fine particles of a volatile gas generated from the melted resin are prevented from adhering to the optical fiber and the optical system and forming a film when the volatile gas solidifies. For this reason, it is possible to prevent deterioration of the optical coupling between the optical fiber and the optical system, and the optical coupling part of the optical module is positively protected.
In the optical module producing method, the step (b) may supply pressurized dry air to the first communication passage.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.